The field is the regeneration of catalyst in a catalyst regenerator vessel.
Fluid catalytic cracking (FCC) is a hydrocarbon conversion process accomplished by contacting hydrocarbons in a fluidized reaction zone with a catalyst composed of finely divided particulate material. The reaction in catalytic cracking, as opposed to hydrocracking, is carried out in the absence of substantial added hydrogen or the consumption of hydrogen. As the cracking reaction proceeds, substantial amounts of highly carbonaceous material referred to as coke is deposited on the catalyst. A high temperature regeneration operation within a regenerator zone combusts coke from the catalyst. Coke-containing catalyst, referred to herein as coked catalyst, is continually removed from the reaction zone and replaced by essentially coke-free catalyst from the regeneration zone. Fluidization of the catalyst particles by various gaseous streams allows the transport of catalyst between the reaction zone and regeneration zone.
A common objective of these configurations is maximizing product yield from the reactor while minimizing operating and equipment costs. Optimization of feedstock conversion ordinarily requires essentially complete removal of coke from the catalyst. This essentially complete removal of coke from catalyst is often referred to as complete regeneration. Complete regeneration produces a catalyst having less than 0.1 and preferably less than 0.05 wt-% coke. In order to obtain complete regeneration, the catalyst has to be in contact with oxygen for sufficient residence time to permit thorough combustion.
Regenerators typically include a vessel having a coked catalyst inlet, a regenerated catalyst outlet and a regeneration gas distributor for supplying air or other oxygen containing gas to the bed of catalyst that resides in the vessel. Cyclone separators remove catalyst entrained in the flue gas before the gas exits the regenerator vessel.
In a bubbling bed regenerator, fluidizing regeneration gas forms bubbles that ascend through a discernible top interface of a dense catalyst bed. Only catalyst entrained in the gas exits the dense catalyst bed with the regeneration gas. The superficial velocity of the regeneration gas is typically less than 1.2 m/s (4.2 ft/s) and the density of the dense bed is typically greater than 320 kg/m3 (20 lb/ft3) depending on the characteristics of the catalyst.
A bubbling bed regenerator may have just one chamber in which air is bubbled through a dense catalyst bed. Coked catalyst is added and regenerated catalyst is withdrawn from the same dense catalyst bed. Relatively little catalyst is entrained in the flue gas exiting the dense bed. Two-stage bubbling bed regenerators have two chambers. Coked catalyst is added to a dense bed in a first chamber and is partially regenerated with air. The partially regenerated catalyst is transported to a dense bed in a second chamber and completely regenerated with air. The completely regenerated catalyst is withdrawn from the second chamber. Some bubbling bed regenerators have deep bubbling beds in which the interface between the dense catalyst phase and the dilute catalyst phase can be at least 7.6 m (25 feet) high.
Sufficient exposure of coked catalyst to regeneration gas is necessary to completely burn coke from the coked catalyst. Sufficient exposure requires thorough mixing of catalyst and regeneration gas and sufficient residence time for the coked catalyst and regeneration gas to be with each other.
Improved methods are sought for ensuring coked catalyst is sufficiently exposed to the regeneration gas.